Civilian and military standards specify a weight range extending from 46.5 kilograms (kg) to 96 kg for people who ought to survive a crash. The strength of bone structure in withstanding intense compression, e.g. as a result of a sudden acceleration, varies significantly within this population range. There is thus a real problem of matching such morphological variation to the strength and damping characteristics of seats, in particular in helicopters. The mass in question can also vary as a function of the number of seats that are actually occupied on a bench seat.
The stroke of an energy absorber therefore needs to be adapted to the entire potential weight range of the occupant(s). If such a stroke is too short, then a heavy occupant runs the risk of being injured since the absorber system comes into abutment, thereby preventing any further damping. On the contrary, if the stroke corresponds to a heavy occupant, then the system will be overdimensioned and the acceleration to which a light occupant will be subjected will not be damped sufficiently.
Certain known seats are fitted with manual adjuster systems enabling the deceleration of the damper to be adapted to the weight of the occupant. That requires human intervention that can lead to adjustment being forgotten or performed wrongly. Such systems are also often heavy, bulky, and expensive.
Energy absorber systems are also known that limit peak downward force so that the peak downward force remains constant during the stroke of the absorber. However variations in weight from one individual to another are not taken into account.